Measurement of Brillouin frequency shift distribution in fiber sensor based on double-edge technique is proposed. Utilizing the characteristic that the edge signal is sensitive to the change of frequency, edge detection technique is proposed, and the system is operated on the best sensitive point by setting the optimum point. From the theoretical analysis, in order to achieve Brillouin frequency shift accuracy of 0.5 MHz, the signal to noise ratio (SNR) required are 65.1127 dB, 37 dB and 31 dB for conventional detection by measuring the maximum signal, single-edge technique, and double-edge technique, respectively. So, for the same SNR, edge techniques can improve the measurement accuracy of Brillouin frequency shift greatly comparing with the conventional detection techniques.